Embodiments in accordance with the present invention relate to a magnetic head and a magnetic storage apparatus, capable of coping with a high areal recording density.
A giant magnetoresistive (GMR) film called a spin-valve has been in use as material for a read head of a HHD (Hard Disk Drive), as progress toward higher magnetic recording densities advances, enabling a read output to be enhanced up to now due to improvement on film makeup. A film makeup of the spin-valve has a structure comprising an antiferromagnetic layer/a pinned ferromagnetic layer/a non-magnetic intermediate layer/a free ferromagnetic layer. As magnetization of the pinned ferromagnetic layer is pinned by an interlayer coupling field occurring to an interface between the antiferromagnetic layer, and the pinned ferromagnetic layer, and the free ferromagnetic layer undergoes magnetization reversal owing to an external field, so that relative orientations of magnetization of the magnetic layers are changed, and electric resistance undergoes a change, thereby detecting a magnetic field. In this case, current flows in a direction parallel to a film plane of the GMR film. In order to achieve a still higher output, R and D have lately been conducted on a CPP (Current Perpendicular to the Plane)—GMR head for causing current to flow in a direction perpendicular to a film plane of the GMR film, and there have since been disclosed various methods including a method for achieving a higher output by forming an insulating layer inside the spin-valve, a method for achieving a higher output by increasing the number of interfaces between respective stacked layers, and so forth.
[Patent Document 1] JP-A No. 204002/2002
[Patent Document 2] JP-A No. 222504/2002
In the case of the CPP-GMR head, upper and lower shields are directly connected to the GMR film, doubling as an electrode, respectively, so that the upper and lower shields each need to fulfill not only the function of a conventional magnetic shield but also the function of the electrode. Further, with a conventional read head, upper and lower shield layers are separated from the spin-valve, respectively, with the intermediary of an insulating gap layer composed mainly of amorphous, so that crystalline structure of the shields poses no problem, however, in the case of the CPP-GMR head, the spin-valve is formed directly on the lower shield, so that the crystalline structure of the shield comes to exert an influence upon properties of the GMR film. Accordingly, a shield material, and film makeup are very important factors for enhancement in the properties of the CPP-GMR head.
An NiFe base alloy, a FeAlSi base alloy, a Co base amorphous alloy, and so forth are well known as (material for) the shields of a read head. The NiFe base alloy, and the FeAlSi base alloy are crystalline, and if those alloys, as they are, are applied to the CPP-GMR head, the crystallinity thereof will exert a large influence upon the properties of the GMR film. Further, in the case of using the Co base amorphous alloy for the shields, there exist problems such as deterioration in the function of the shields as the electrodes, owing to high resistance of the Co base amorphous alloy, deterioration in heat dissipation properties, and susceptibility to occurrence of read instability attributable to the shields.
A problem with a conventional CPP-GMR head lies in that even if the GMR film is formed on a NiFe shield normally as thick as not less than 1 μm, stable and excellent properties cannot be obtained. With the GMR film of the so-called confined current path type, in particular, there is a tendency that an area-resistance product becomes high while a magnetoresistance (MR) ratio becomes low. If the area-resistance product is high, read head performance at high frequency deteriorates as enhancement in recording density advances, and the GMR film as described is therefore not recommendable for application to the magnetic head. The GMR film exhibiting a high MR ratio at a low area-resistance product is desirable. With the confined current path type CPP-GMR head, use is made of an extremely thin oxidized film having a structure with fine pin holes for causing current to flow locally in the direction of a film thickness. The structure of the extremely thin oxidized film is a major factor for determining the area-resistance product as well as the MR ratio of the CPP-GMR head. As the crystalline structure of the lower shield is considered to have a large effect on the formation of the extremely thin oxidized film, how to control the crystalline structure of the GMR film is important.